Method of forming multilayered electrodes for ferroelectric devices consisting of conductive layers and interlayers formed by chemical reaction

Abstract

A ferroelectric device is constructed using a bottom electrode composed of a conducting oxide such as RuOx, on a substrate such as silicon or silicon dioxide. A ferroelectric material such as lead zirconate titanate (PZT) is deposited on the bottom electrode, and a conducting interlayer is formed at the interface between the ferroelectric and the electrode. This interlayer is created by reaction between the materials of the ferroelectric and electrode, and in this case would be Pb2Ru2O7-x. A conductive top layer is deposited over the ferroelectric. This top layer may be a metal, or it may be the same type of materials as the bottom electrode, in which case another interlayer can be formed at the interface. A device constructed in this manner has the property of lower degradation due to fatigue, breakdown, and aging.

What is claimed is: 
     
       1. A method of making a ferroelectric device comprising the steps of: a) depositing a conducting oxide on a substrate to provide a ceramic electrode;   b) depositing a layer of ferroelectric material on said ceramic electrode to produce an interface between the ferroelectric layer and the ceramic electrode;   c) annealing said electrode and said ferroelectric layer to react the conducting oxide with the ferroelectric layer to produce a conductive interlayer at the interface; and   d) depositing a conductive top electrode over said layer of ferroelectric material.   
     
     
       2. A method according to claim 1 wherein said ferroelectric material is selected to react with said ceramic electrode from the group consisting of lead zirconate titanate and ferroelectric compounds of the form ABO 3  and AB'B"O 3 , where A belongs to the group of Pb, Ba, Bi, Li, La, or Sr, and where B belongs to the group of Ti, Nb, Ta, Mg, Sn, W, or Zr. 
     
     
       3. A method according to claim 1 wherein said ceramic electrode is a conducting oxide selected to react with said ferroelectric layer from the group consisting of RuO x , ReO x , RhO x , IrO x , and Oso x . 
     
     
       4. A method according to claim 1 wherein said conductive interlayer includes a conducting compound selected from the group consisting of the compounds of the form A 2  M 2  O 6 , A 2  M 2  O 7-x  and AMO 3  which is formed by the reaction between the ceramic electrode and said ferroelectric material, where A is selected from the group consisting of Pb, Ba, Sr, and La, and where M is selected from the group consisting of Ru, Re, Rh, Ir, and Os. 
     
     
       5. A method according to claim 4 wherein said ceramic electrode is a conducting oxide selected from the group consisting of RuO x , ReO x , RhO x , IrO x , and OsO x , and wherein said ferroelectric material is selected from the group consisting of lead zirconate titanate and ferroelectric compounds of the form ABO 3 , where A is from the group consisting of Pb, Ba, Bi, Li, La, and Sr, and where B is from the group consisting of Ti, Nb, Ta, Mg, Sn, W, and Zr, so that the ceramic electrode will react with the ferroelectric layer to produce the conductive interlayer. 
     
     
       6. A method according to claim 1 further including the step of forming a second interlayer located between said layer of ferroelectric material and said top layer, said second interlayer being composed of a conducting compound. 
     
     
       7. A method according to claim 1 wherein said substrate is composed of a material selected from the group consisting of silicon, sapphire, silicon oxide, silicon with a silicon oxide coating, and gallium arsenide. 
     
     
       8. A method according to claim 1 wherein said steps of depositing are performed by a technique of the class of sputtering, CVD, sol-gel, electron beam evaporation, metallorganic decomposition, and laser ablation.